After four years of work in a former iron mine a half-mile underground, the Main Injector Neutrino Oscillation Search collaboration celebrated a milestone for the ambitious MINOS particle physics experiment. On June 5, technicians erected the last of 485 house-high detector planes of steel and plastic in the Soudan Underground Laboratory in Soudan, Minnesota.

"The technicians carried out the work faster and less expensively than estimated," said Bill Miller, responsible for hiring and supervising the technicians at the lab. "We used six people less than the original labor estimate, and yet we ended up installing six planes per week, more than the original projection. We had a really excellent crew of workers. That was the key to our success."

Overall, the four-year project finished on schedule and on budget. The faster-than-expected installation made up for time lost during the excavation of the
cavern that hosts the experiment.

The whole detector is about 100 feet long and consists of massive planes that are lined up like the slices in a loaf of bread. Each plane consists of a sheet of steel, about 25 feet high and one inch thick, covered on one side with a half-inch layer of scintillating plastic. Because all material had to enter the cavern through
an old narrow shaft, the 6,000-ton detector arrived in pieces not more than seven feet in width.

"It was like building a ship in a bottle," said MINOS spokesperson Stanley Wojcicki, physics professor at Stanford University. "We needed to bring all the material underground and assemble it right there. It was a real challenge to coordinate the logistics."

The project began in July 1999, with the groundbreaking for the cavern that
now hosts the detector. The installation of the first plane occurred in August
of 2001. Because of limited storage space in the underground area, the work
crew relied on continuous delivery of steel sections through the shaft.

"Because the transportation cage was used during the day for tourists visiting
the old iron mine, we lowered the pieces underground during the second shift
at night," said Fermilab physicist Jeff Nelson, who explained that the Soudan
mine is a State Park with 30,000 visitors per year. "We had a crew of three on
the surface, working year-around. Over the two years, only three shifts were
canceled due to weather."

To carry out the two-year project, the Soudan
laboratory hired about 30 technicians, many of
whom it recruited from among the 1,300 people
that were laid off when a steel company stopped
mining in Soudan in 2001. Now, with the detector
installation almost complete, workers are again
forced to change jobs.

"It was a rather anticlimactic end of the project.
When the last plane went up we laid off 17 people,"
said Miller, who has worked at the underground lab
for 17 years. Many of the laid-off technicians have
been able to secure summer jobs, but with another
mine shutting down and laying off 600 people the
prospects are less than rosy.

During the installation, technicians worked in two
ten-hour shifts and accounted for about 75 percent
of the total manpower. A mix of graduate students,
postdocs and senior scientists from many of the
32 MINOS institutions from six countries—Brazil,
France, Greece, Russia, United Kingdom and
the United States—significantly contributed to the
work at Soudan as well, with a special emphasis
on the installation of the electronics and the
commissioning of detector planes within days of
their installation.

Work on the detector, however, was not limited
to the Soudan mine. A number of university and
laboratory groups in the U.S., UK, and Greece
worked at their home institutions on the production
of detector components, representing more than
half the cost of the detector. In a carefully
coordinated effort, the groups built and tested the
pieces of the plastic scintillator system and then
shipped them to the Soudan mine for installation.

In about a month, the whole detector will be ready
to observe cosmic rays and atmospheric neutrinos,
which easily penetrate the surface of the earth and
reach the MINOS detector deep underground. For
the last nine months, scientists have already used
half of the detector to record particle interactions.
In April, the MINOS collaboration reported its
first scientific results, the identification of twelve
atmospheric neutrino events.

Over the next two years MINOS scientists will
focus on the so-called CPT test of atmospheric
neutrino interactions, looking for differences in the
interactions of matter and antimatter. Unlike earlier
neutrino experiments such as Super-Kamiokande,
MACRO and Soudan 2, the MINOS detector
features a 1.5-Tesla magnet that allows scientists
to distinguish between signals caused by neutrinos
and antineutrinos.

MINOS will enter its next stage in 2005, when
scientists will use the detector to “catch” neutrinos
created 450 miles away at Fermilab in Batavia,
Illinois. The beam line creating the neutrinos is
under construction. When ready, about five trillion
muon neutrinos per year will travel straight through
rock and traverse the detector in Soudan, but only
about 1,500 of the rarely-interacting particles are
predicted to leave a trace inside the detector.
Scientists will use the long-distance experiment
to study the oscillation of muon neutrinos into
electron neutrinos or tau neutrinos under laboratory
conditions.

"We really appreciate the work the technicians
did for us," said Nelson, who has spent most of his
last two years in Minnesota. "Now it has gone from
beehive activity to taking care of the last details."

He and his colleagues will make sure that physics
data will keep the lab abuzz.